Increasing Stirring Speed Research Articles

Photocatalytic and Luminescent Properties of SrMoO4 Phosphors Prepared via Hydrothermal Method with Different Stirring Speeds

To probe the potential utilities in the photocatalyst and luminescent materials, a series of SrMoO4 samples have been prepared via the hydrothermal preparation with different stirring speeds. These SrMoO4 samples were characterized using X-ray diffraction analysis, scanning electron microscopy, UV–diffuse reflection spectroscopy (UV–vis). It has been found that the lattice parameters and [MoO4] tetrahedron distortion of SrMoO4 samples are increased with the increased stirring speed in the process of hydrothermal preparation. By changing the stirring speeds, spindle and succulent-like morphologies have been obtained. UV–vis results show that the band gaps of SrMoO4 samples are sensitive to the stirring speed. As for the luminescent and photocatalytic properties, our experimental results clearly suggest that, compared with those samples without stirring, the luminescent and photocatalytic activities are enhanced with stirring in the hydrothermal preparation. The photodegradation of methyl blue (MB) over SrMoO4 system increases from 30% to 50% with stirring, which may be related to small band gaps and porous surfaces. Our results indicate that stirring may be one important technique to improve the photocatalytic properties, especially in the process of hydrothermal method.

Study on the Regeneration of Basic Aluminum Sulfate SO2-Rich Solution by Vacuum Desorption

Basic aluminum sulfate (BAS) wet flue gas desulfurization (FGD) is a promising renewable process used to remove sulfur dioxide (SO2) from flue gas, in which the regeneration of BAS SO2-loaded solution is of great importance for the reuse of BAS solution. In this paper, a novel regeneration method by vacuum desorption was developed to achieve superior regeneration performance for a BAS-rich solution. The operating parameter effect on SO2 desorption performance was thoroughly investigated in a lab-scale reactor. The experimental results demonstrated that the great decrease of pressure could significantly improve the regeneration performance, and high desorption temperature was favorable for SO2 desorption. Furthermore, it is worth determining the optimum components of a BAS-rich solution and initial sulfite concentration, considering the contradiction between the SO2 absorption performance and the regeneration performance. The increase of stirring speed in the liquid had a considerable positive effect on SO...

Effects of polymerization conditions on particle size distribution in styrene‐graphite suspension polymerization process

ABSTRACTSuspension polymerization in the presence of graphite has been studied in order to determine the effects of some operational parameters on the particle size distribution (PSD). The results showed that, with increasing graphite content, the particle size of the polystyrene/graphite (PS/G) beads increased. Moreover, instability of the suspension polymerization system was found at high amounts of graphite. With increasing initiator concentration, the particle size of the polymer beads increased and the PSD became slightly narrower. Changing the concentration of the suspending agent proved to be an efficient way of controlling the particle size, although its increase led to a broadening of the PSD. Adding the suspending agent in two portions at different times decreased the particle size, maintained a lower concentration of suspending agent, and kept the suspension polymerization system stable. Adjusting the stirring speed proved to be a very efficient means of manipulating the PSD of the PS/G composite beads. The Sauter mean diameter decreased and the PSD was broadened with increasing stirring speed; 400 rpm was identified as an appropriate value to obtain polystyrene/graphite beads with desirable particle size and distribution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44270.

Effects of Temperature and External Force on the Stereocomplex Crystallization in Poly(lactic acid) Blends

AbstractAn investigation of the effects of temperature and external force on the stereocomplex‐type poly(lactide acid) formation between equimolar of poly(L‐lactide acid) (PLLA) and poly(D‐lactide acid) (PDLA) was conducted. Wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) analysis indicated that exclusive stereocomplex‐type poly(lactide acid) (sc‐PLA) with relatively high crystallinity could be obtained at lower (0°C) temperature. During solution mixing process, increasing stirring speed within range 0–200 rpm was conductive to the formation of sc‐PLA. However, excessive stirring speed gave rise to a decrease in sc‐PLA production. During solvent evaporation process, addition of shaking could effectively improve formation of sc‐PLA, wherein crystallinity of sc‐PLA approached the maximum value as shaking speed reach 100 rpm. These suggest that lower temperature and appropriate external force are positive to the formation of sc‐PLA in PLLA/PDLA blends.

STUDY THE EFFECT OF STIRRING SPEED AND PARTICLE SIZE ON THE TENSILE STRENGTH OF THE ALUMINUM MATRIX COMPOSITE (Al6063-2wt% Al2O3

This research examines the effect of stirring speed and size of the alumina particles added of Al6063 on the tensile properties of the Al-6063 reinforced by Al2o3 Particles using the program MINITAB 16. Stir casting method has been used to produce a composite material, the ingot was smelted, vortex of molten metal were created by stirring using different speeds (1000,900,800,700,600 rpm) and a fixed period of time (10min.) and then alumina particles of (2% wt) and different sizes of (700,500,355,250,106 μm) were added. It was concluded that the best tensile strength of (107.5989 Mpa) can be obtained when the variables were (X1 = 1000 rpm) (X2 =374.4μm). The lights value of X1 and X2, obtained using the programs, was used in practice giving tensile strength (109 Mpa) which it nearly similar to that obtained by program. Also results show that the variables Stirring Speed (X1) & Particle Size (X2) have a significant effect on tensile strength. Moreover, the tensile strength increases with increasing stirring speed. Alumina particle size increases the tensile strength until the particles reach the size of particulate (335μm) and after that go down.

Morphology and size control of gelatin/hyaluronic acid composite microsphere for drug delivery

Composite microspheres based on gelatin (Gel) and hyaluronic acid (HA) were prepared by an emulsion–coagulation method with glutaraldehyde as a crosslinker. The influences of stirring speed, crosslinker concentration, HA content and water/oil ratio on the particle size and surface morphology were investigated. The Fourier transform infrared spectra characterisation indicated that Gel and HA were crosslinked successfully by the glutaraldehyde. The in vitro release behaviours of 5-fluorouracil (5-FU) from Gel/HA microspheres were also studied. The results showed that the adhesion and agglomeration phenomena were apparent when the HA content reached 10.0 wt-%. The particle diameter of the microspheres decreased greatly with increasing stirring speed; however, the adhesion of smaller microspheres could be observed when the stirring speed reached 800 rev min− 1. The effect of crosslinker concentration on the particle size was not significant, but the dispersion degree of the Gel/HA microspheres decreased with decreasing crosslinker content. The particle size of the microspheres gradually became uniform with the increase of the water/oil ratios. The dispersion and surface smoothness level could be improved by optimising the experimental conditions. The cumulative drug release of 5-FU from the microspheres decreased with increasing glutaraldehyde content. The results of 5-FU release kinetics from Gel/HA microspheres indicated Fickian diffusion.

Chitosan microespheres elaboration to growth factors release

Event Abstract Back to Event Chitosan microespheres elaboration to growth factors release Katia Jarquin1, Jesús Arenas2, Gabriela Piñon1, Miguel A. Herrera1, Beatriz Hernández1, Erick Sánchez1, Armando Zepeda1, Andrés Sánchez3, Jorge E. Miranda3 and Andrés E. Castell1 1 Facultad de Medicina, UNAM, Biología Celular y Tisular, Mexico 2 Instituto de Física, UNAM, Materia Condensada, Mexico 3 UAM-Xochimilco, Sistemas Biológicos, Mexico Introduction: Exists various release models of active ingredients such as liposomes, nanoparticles and microparticles. In the microspheres, the active ingredient is released by diffusion and also by the microsphere degradation[1]. So many variables can be found during the construction of microspheres such as type of active tense, relation between the dispersed phase and the continuous phase in the working solution, solvent condition and the percentage of the active ingredient encapsulated[2]. As a result, it is important to standardize the conditions of the microsphere production in order to manufacture and characterize chitosan microspheres. Method: Furthermore, in order to verify the proper concentration of SPAN 80, different concentrations were used. 0.25, 0.5 and 1% of SPAN 80 were mix in 25ml of mineral oil and stir at 12.2 rpm in an IKA Ultraturrax. In one hand, a 2% chitosan solution in 5% acetic acid were prepared and placed in a 5ml syringe; which was added to SPAN 80 solution drop by drop and stirred for 5, 10 and 15 minutes. Later, SPAN/ chitosan solutions were first stirring for 30 minutes and fixed with glutaraldehyde and finally stirred for 6 hours. Chitosan/SPAN solution was centrifuged and washed with hexane and distilled water. Finally, the microspheres of chitosan were incubated with BMP 2 and VEFG-1 in order to evaluate bone marrow stem cell diffentiation to osteoblats . Results and Discussion: It was observed that stirring at 12.2 rpm for 10 minutes was the optimum speed for the production of homogeneous microspheres in form and size. The increase of stirring speed has induced the microspheres breakage, while the decreased stirring speed has induced the development of bigger microspheres. Regarding the SPAN concentration, the 1% SPAN solution was the one which has induced the formation of microspheres from 5 to 10 microns, according to the analysis made by Scanning Electron Microscopy, Flow cytometry and the Zetasizer. Bone marrow cells incubated with microspheres were positive to alkaline phosphatase and osteopontin. This investigation was supported by DGAPA PAPIIT IN218315; The first author is a student of Posgrado en Ciencias Médicas y de la Salud.; Francisco Pasos Nájera and Raquel Guerrero Alquicira for their technical assistance in this investigation

Leaching of Copper from Metal Powders Mechanically Separated from Waste Printed Circuit Boards in Chloride Media Using Hydrogen Peroxide as Oxidant

The dissolution of copper from waste printed circuit boards in chloride media using hydrogen peroxide as oxidant was carried out. The effects of stirring speed, temperature, solid/liquid ratio and concentrations of HCl and H2O2 on the leaching of copper were investigated. The copper extraction increased significantly with the increase of HCl concentration. H+ and Cl− ions both improved the leaching of copper from waste printed circuit boards and had the synergetic effect on copper dissolution. The H2O2 was the main reagent which made possible the leaching of metallic copper from waste printed circuit boards in acidic chloride solutions. The copper extraction also increased with the increase of stirring speed, temperature and solid/liquid ratio. Finally, a reaction mechanism was proposed as well.

The Effect of Process Parameters on the Mechanical Properties of A356 Al-Alloy/ZrO<sub>2</sub> Nanocomposite

In this study the effect of zirconia (ZrO2) nanoparticles (40 nm) in reinforcing A356 aluminum alloys as a base metal matrix were investigated. Zirconia nanopowders were stirred in the A356 matrix with different fraction ratios ranging from (0, 1, 2, 3, 5%) by weight at variable stirring speeds ranging from (270, 800, 1500, 2150 r.p.m) at a mushy zone (600°C) and liquid state (700°C) using a constant stirring time for one minute. The microstructure revealed the change of grains from dendritic to spherical shape with increasing stirring speed. The Scanning Electron Microscopy of the fractured surface revealed the presence of nanoparticles at the interdendritic spacing of the fracture surface and was confirmed with EDX analysis of these particles.The results of the study showed that the mechanical properties (strength, elongation and hardness) using ZrO2 as reinforcements were increased at the following parameters: 1500 r.p.m stirring speed in semi-solid state (600oC) and adding 3 wt.% of ZrO2.

Study on uranium peroxide precipitation in a continuous fluidized-bed reactor with mechanical stirring

This study provides the results obtained from the experiments carried out in a specially adapted continuous fluidized-bed reactor equipped with a multi-impeller stirring device. The influence of operating parameters on yellow cake precipitation as uranium peroxide was studied. The effects of stirring speed and feed flow rate were investigated. An increased stirring speed decreased the agglomerate mean size, mainly due to the strong negative influence of the shear rate on the agglomeration kinetics. In addition, the nominal capacity of the fluidized-bed reactor was doubled, while the uranium concentration level was strictly respected at the outlet. The experimental results obtained in this study will be used for process modeling in a further study.

Nanoreinforced Cast Al-Si Alloys with Al2O3, TiO2 and ZrO2 Nanoparticles

This study presents a new concept of refining and enhancing the properties of cast aluminum alloys by adding nanoparticles. In this work, the effect of adding alumina (Al2O3), titanium dioxide (TiO2) and zirconia (ZrO2) nano-particles (40 nm) to the aluminum cast alloy A356 as a base metal matrix was investigated. Alumina, titanium dioxide and zirconia nano-powders were stirred in the A356 matrix with different fraction ratios ranging from (0%–5%) by weight at variable stirring speeds ranging from (270, 800, 1500, 2150 rpm) in both the semisolid (600 °C) and liquid (700 °C) state using a constant stirring time of one minute. The cast microstructure exhibited change of grains from dendritic to spherical shape with increasing stirring speed. The fracture surface showed the presence of nanoparticles at the interdendritic spacing of the fracture surface and was confirmed with EDX analysis of these particles. The results of the study showed that the mechanical properties (strength, elongation and hardness) for the nanoreinforced castings using Al2O3, TiO2 and ZrO2 were enhanced for the castings made in the semi-solid state (600 °C) with 2 weight% Al2O3 and 3 weight% TiO2 or ZrO2 at 1500 rpm stirring speed.

Cooling crystallization of aluminum sulfate in pure water

This study investigated the cooling crystallization of aluminum sulfate to explore the basic data for the recovery of aluminum resources from coal spoil. First, the metastable zone width (MSZW) of aluminum sulfate was reported. A parallel synthesis platform (CrystalSCAN) was used to determine the solubility from 10°C to 70°C, and an automatic lab reactor (LabMax) equipped with focused beam reflectance measurement (FBRM) was adopted to determine the supersolubility. The effects of operating variables on MSZW were experimentally explored. Results show that the MSZW of aluminum sulfate decreases with increasing stirring speed, while it increases with increasing cooling rate.Second, the continuous crystallization kinetics of aluminum sulfate was investigated in a laboratory-scale mixed-suspension mixed-product removal (MSMPR) crystallizer at a steady state. Growth kinetics presented size-dependent growth rate, which was well fitted with the MJ3 model. Both the growth rate (G) and the total nucleation rate (BTOT) were correlated in the power law kinetic expressions with good correlation coefficients.Third, aluminum sulfate products were modified by sodium dodecylbenzenesulfonate (SDBS). Crystals with large sizes and regular hexagonal plate morphologies were obtained. These crystals reveal that SDBS can inhibit crystal nucleation and promote crystal growth.

LEACHING OF MALACHITE ORE IN AMMONIUM SULFATE SOLUTIONS AND PRODUCTION OF COPPER OXIDE

Malachite ore is one of the most important of oxidized copper ores. Copper production can be performed by using this ore. In this work, the leaching kinetics of malachite in ammonium sulfate solutions was investigated, and metallic copper was recovered by a cementation method from the resulting actual leach solution. Copper (II) oxide was prepared by an isothermal oxidation method from the cement copper. In the leaching experiments, the effects of reaction temperature, particle size, and stirring speed on copper leaching from malachite ore were studied. In the cementation experiments, metallic zinc was used as the reductant metal to recover the copper from the solution. Thermal oxidation of cement copper was performed under isothermal conditions. It was found that the leaching rate increased with increasing stirring speed and temperature, and decreased with particle size. It was observed that the leaching reaction fit to diffusion through the product layer. The activation energy of the leaching process was determined to be 25.4 kJ/mol. It was determined that the copper content of the metallic product obtained by the cementation method increased up to 96%. It was found that copper oxide prepared from cement copper had a tenorite structure.

A Novel Approach for Analyzing the Dissolution Mechanism of Solid Dispersions

To analyze the dissolution mechanism of solid dispersions of poorly water-soluble active pharmaceutical ingredients (APIs), to predict the dissolution profiles of the APIs and to find appropriate ways to improve their dissolution rate. The dissolution profiles of indomethacin and naproxen from solid dispersions in PVP K25 were measured in vitro using a rotating-disk system (USP II). A chemical-potential-gradient model combined with the thermodynamic model PC-SAFT was developed to investigate the dissolution mechanism of indomethacin and naproxen from their solid dispersions at different conditions and to predict the dissolution profiles of these APIs. The results show that the dissolution of the investigated solid dispersions is controlled by dissolution of both, API and PVP K25 as they codissolve according to the initial API loading. Moreover, the dissolution of indomethacin and naproxen was improved by decreasing the API loading in polymer (leading to amorphous solid dispersions) and increasing stirring speed, temperature and pH of the dissolution medium. The dissolution of indomethacin and naproxen from their amorphous solid dispersions is mainly controlled by the surface reaction, which implies that indomethacin and naproxen dissolution can be effectively improved by formulation design and by improving their solvation performance. The chemical-potential-gradient model combined with PC-SAFT can be used to analyze the dissolution mechanism of solid dispersions and to describe and predict the dissolution profiles of API as function of stirring speed, temperature and pH value of the medium. This work helps to find appropriate ways to improve the dissolution rate of poorly-soluble APIs.

Erosion–corrosion resistance of electroplated Co-Pd film on 316L stainless steel in a hot sulfuric acid slurry environment

A Co-Pd film was deposited on 316L stainless steel by electroplating. The erosion–corrosion behavior of the Co-Pd plated samples in hot sulfuric acid solution with SiO2 particles was investigated. The results showed that there was a significant synergistic effect between erosion and corrosion. At higher stirring speed, even in such strong corrosive environment the erosion–corrosion rate of Co-Pd plated samples was controlled mainly by the erosion resistance. The erosion–corrosion resistance of pure Pd plated sample decreased rapidly with increasing stirring speed, whereas that of Co-Pd plated sample kept almost stable under the tested conditions due to the high micro-hardness and good corrosion resistance of the film.

Microstructural characteristics and mechanical properties of Al-2024 alloy processed via a rheocasting route

This article reports the effects of stirring speed and T6 heat treatment on the microstructure and mechanical properties of Al-2024 alloy synthesized by a rheocasting process. There was a decrease in grain size of α-Al particles corresponding to an increase in stirring speed. By increasing the stirring speed, however, the globularity of matrix particles first increased and then declined. It was also found that the hardness, compressive strength, and compressive strain increased with the increase of stirring speed. Microstructural studies revealed the presence of nonsoluble Al15(CuFeMn)3Si2 phase in the vicinity of CuAl2 in the rheocast samples. The required time for the solution treatment stage was also influenced by stirring speed; the solution treatment time decreased with the increase in stirring speed. Furthermore, the rheocast samples required a longer homogenization period compared to conventionally wrought alloys. Improvements in hardness and compressive properties were observed after T6 heat treatment.

Influence of different formulations and process parameters during the preparation of drug-loaded PLGA microspheres evaluated by multivariate data analysis.

The main objective of this study was to evaluate the influence of the formulation and process parameters on PLGA microparticles containing a practically insoluble model drug (ibuprofen) prepared by the o/w solvent evaporation method. Multivariate data analysis was used. The effects of altered stirring speed of a mechanical stirrer (600, 1000 rpm), emulsifier concentrations (PVA concentration 0.1 %, 1 %) and solvent selection (dichloromethane, ethyl acetate) on microparticle characteristics (encapsulation efficiency, drug loading, burst effect) were observed. It was found that with increased stirring speed, the PVA concentration or the use of ethyl acetate had a significantly negative effect on encapsulation efficiency. In addition, ethyl acetate had an adverse effect on the burst effect, while increased stirring speed had the opposite effect. Drug load was not affected by any particular variable, but rather by the interactions of evaluated variables.

Pore structure of the phenolic porous material and its mechanical property

To enlarge the knowledge about the control methods of pore size of phenolic porous material and to know the effect of pore size on its mechanical property, experiments were carried out. On the basis of the theory of bubble nucleation, large stirring speed can overcome the surface energy of bubble formation and the nucleating agent can provide a large number of nucleation sites for foaming system. We adopted the methods of accelerating the stirring rate and adding nucleating agent to improve bubble nucleation. Pore size, size distribution and the effects of stirring speed and nucleating agent concentration on them were investigated by scanning electron microscope and computerized image analysis program. Results showed that with the increase of stirring speed, the mean pore size decreases from 246 to 138 µm and the structural homogeneity of phenolic porous material was improved obviously. The nucleating agent has a great effect on the pore structure and optimal amount (5%) at which the pore size is small in level of micrometer and has a good distribution. In addition, the compression testing was carried out by Universal Testing Machine and the test results suggested that the change of micrometer pore structure improves the compression strength of porous material effectively.

Increasing synthesis yield of K‐doped tungsten oxide nanowire using stirred hydrothermal reactor and its near‐infrared reflectance property

One-dimensional nanostructured oxides are typically synthesised by the hydrothermal method in a small pressurised reactor under static conditions that usually results in a low synthesis yield. In this reported work, K-doped tungsten oxide (K2W4O13) nanowires were synthesised under stirred hydrothermal treatment of hydrous K2W4O13 precursor in the presence of K2SO4 employed as the shape-directing agent to promote the formation of nanowires. Under static conditions (0 rpm), only 24.6% yield was obtained. The yield was significantly increased with the increase of stirring speed. The yield of 90.3%, almost four times the static condition, was obtained when synthesised under continuous stirring at 500 rpm. The samples synthesised from both the conditions have the same crystal structure, which is K2W4O13. However, the difference in particle morphology was observed; the average diameter of 11.4 ± 0.3 nm and the length up to several hundred micrometres were obtained from the stirred condition, while more irregularities of the nanowires (average diameter of 7.1 ± 1.1 nm and very diverse length) were obtained under static conditions. The more uniformity observed under stirred hydrothermal conditions is attributed to the more uniform crystallisation process attained under the stirring condition. A high near-infrared (NIR) reflectance of 91.3% suggests its NIR shielding ability.

Negative Impact of High Stirring Speed in Laboratory-Scale Three-Phase Hydrogenations

An increase in stirring speed is generally considered to be an a priori means of reducing external mass-transfer limitations in fast three-phase hydrogenations that are performed in a stirred tank. We provide experimental evidence for a 300-mL stirred reactor that, above a certain impeller speed, the efficiency of gas–liquid mass-transfer decreases, resulting in the decreased reaction rate. The phenomenon is attributed to the high degree of gas recirculation with large cavities behind the blades. The recirculation may decrease hydrogen concentration in the remainder of the tank, thus decreasing the concentration gradient that controls mass transfer. The model reaction in this work was 2-methyl-3-butyn-2-ol semihydrogenation with Lindlar catalyst Pd–Pb/CaCO3. The test impellers were a Rushton turbine, a down-pumping pitched blade turbine, and up-pumping A340 impellers. The kinetic experiments were combined with the measurement of volumetric gas–liquid mass-transfer coefficient, flow pattern analysis and im...